The silence of the vast Danube delta is broken only by the sound of a few Ukrainian launches manned by Kalashnikov-toting soldiers, who keep an eagle eye on all activity in the area. They have been particularly vigilant since the Kiev government began building a navigation canal in the Bystroye estuary in the heart of the delta.

Access to the canal, which lies between southern Ukraine and southeastern Romania, is forbidden, and any attempt to reach it is forcefullydiscouraged. Kiev is determined to keep its scheme as secret as possible, even thought it has prompted considerable concern on the part of ecological organisations, Romania, Europe and Unesco, which has put the delta on its World Heritage list.

According to the experts, the Danube delta is indeed very much at risk. The dredging work started by Ukraine in May will endanger a reserve of flora and fauna that is unique in Europe.

After several Dutch contractors had turned down offers to work on the canal, the Hamburg-based company Josef Moebius Bau took on the project. Kiev contends that the Bystroye canal will provide Ukraine with an extra outlet to the Black Sea. But at what cost?

In order to be navigable, the canal will be 10m deep. Ecological associations have already reported that several hundred rare birds' eggs have been destroyed. But the worst is yet to come: the volume of water sucked into the navigation canal may lower the water level in protected areas on the Romanian side of the delta. The subtropical Letea forest, for example, which is the jewel of the delta, and several islets may not survive.

The World Wildlife Fund argues that, despite alternative routes connecting the Ukrainian part of the Danube to the Black Sea, the area is being destroyed in violation of at least 11 international conventions to which Ukraine is a signatory. The WWF also claims that the multimillion-dollar scheme threatens the habitat of more than 280 bird species and fish breeding grounds, thus jeopardising the region's fishing and tourism industries.

Fishermen in the village of Periprava, in the northern Romanian part of the delta, are also up in arms about the project. One of them, Vasile Fedetov, says: "I heard about the whole thing on telly. We're very cut off here. All we know about is fishing and our patch of delta. I didn't even know what was going on a few kilometres away, on the Ukrainian side."

Few villages are as remote as Periprava, which was built on reed-beds by the Lipovenians, a people of Russian origin who moved to the Danube delta in the 17th century. It is slowly dying as members of its younger generation move to towns on the Romanian coast of the Black Sea. The lucky ones get as far as Bucharest. But the destination that most attracts young fishermen from the delta is Italy, where they can work illegally.

"What is there for us to do here?" asks Fedotov. "I get up at 2am, prepare my equipment and my boat, and set off. I fish until 9am, at which point I hurry to sell my catch. There are days when I manage to catch 30 kilos of fish, but on other days I come back with only 5 kilos. After the fall of communism, they changed the fishing regulations: we're being throttled."

Following pressure from the European Union, Romania introduced Draconian controls on the Danube delta. The Lipovenian fishermen, erstwhile kings of the delta, have been forced to give up their old habits. They have to keep strictly to their fishing quotas, otherwise they lose their licence. Areas where fishing is allowed are patrolled day and night, while protected zones are completely out of bounds.

Romania fears that its efforts to protect the delta are being jeopardised by the building of a navigation canal. The Romanian prime minister, Adrian Nastase, has launched a "personal appeal" to his Ukrainian opposite number, Viktor Yanukovich. He has also deplored "the lack of bilateral consultations".

But the campaign against the Bystroye canal is not being conducted on purely ecological grounds. There is also the problem of how to divide up the reportedly oil-rich continental shelf of the Black Sea - an issue that was left in abeyance after the two countries signed a treaty of friendship. Le Monde